1. Field of the Invention
The present invention relates to impact grinders, hammermills, or the like, and particularly to a screenless hammermill that can be used to reduce the size of material to a desired dimension.
2. Background Art
A number of different industries rely on impact grinders or hammermills to reduce materials to a smaller size. Hammermills are often used to process forestry and agricultural products as well as to process minerals, and for recycling materials. Specific examples of materials processed by hammermills include ore, limestone, coal, railroad ties, lumber, limbs, brush, grains, and even automobiles. Once reduced to the desired size, the material passes out of the housing of the hammermill for subsequent use and further processing. Exemplary embodiments of hammermills are disclosed in U.S. Pat. Nos. 5,904,306; 5,842,653; 5,377,919; and 3,627,212, all of which are incorporated herein in their entireties.
Hammermills—also generally referred to as crushers or shredders—typically include a steel housing or chamber containing a plurality of hammers mounted on a rotor and a suitable drive train for rotating the rotor. As the rotor turns, the correspondingly rotating hammers come into engagement with the material to be comminuted or reduced in size. Hammermills typically use grates formed into and circumscribing a portion of the interior surface of the housing. The size of the particulate material is controlled by the size of the screen apertures against which the rotating hammers force the material. Unfortunately, in prior art hammermills, material can “short circuit” or by-pass the hammers by being forced through the apertures in the grates or screens before being thoroughly processed or sized.
Furthermore, the prior art grates or screens can become restricted and plugged with the materials being reduced, which, in turn, reduces the throughput and efficiency of the hammermill. In particular, wood that has a “stringy bark,” such as poplar, hickory, and eucalyptus, is very problematic for the grates and thus is not effectively reduced using a prior art hammermill because materials tend to straddle the apertures and to build up therein, resulting in the apertures becoming plugged or partially deformed which does not allow material of a desired size to pass through the plugged or deformed aperture(s) and reduces throughput and efficiency of the hammermill. Thus, the higher energy costs and the cost of the need for frequent repair and replacement of the grate or screen represents a significant ongoing financial outlay.
There is a need, therefore, for an improved hammermill adapted for use with any desired materials to be processed, and which will increase the likelihood of the materials passed therethrough being thoroughly processed, at least to the extent desired.